1. Field of the Invention
This invention relates to a pixel electrode substrate to be used for a reflection type liquid crystal apparatus and to a liquid crystal apparatus using such a pixel electrode substrate for displaying pictures and characters as well as to a display apparatus using such a liquid crystal apparatus. More particularly, it relates to a reflection type liquid crystal apparatus comprising a pair of opposing substrates and liquid crystal filling the gap between the substrates, one of which carries thereon a plurality of patterned pixel electrodes for receiving light emitted from the other substrate.
2. Related Background Art
The world has entered a so-called multi-media age and devices and equipment for exchanging pictorial information for communication purposes are playing an ever-increasingly important role, Liquid crystal apparatus are attracting attention because they can be realized in a thin and portable form and consume only a small amount of power so that the industry of manufacturing such devices has grown as one of the major industries, comparable with the semiconductor industry.
Liquid crystal apparatus are at present popularly used for so-called notebook size personal computers having a size as short as ten inches. Additionally, liquid crystal is expected to play a major role in displays of electronic work stations and home television sets that typically comprise a large display screen. However, a large display screen involves high manufacturing cost and is required to meet rigorous electric requirements for driving the large screen. As a rule of thumb, the manufacturing cost of a liquid crystal display panel is said to be proportional to the square or cube of the size of the screen.
Thus, as an alternative, a projection system designed to use a small liquid crystal panel and enlarge the image formed on it has been proposed. Such a system is made feasible mainly due to the recent development of finely sized semiconductor devices that operate excellently and can be manufactured at low cost.
In view of the recent technological development, there is an increasing demand for small TFTs provided with a satisfactory drive power to be used in liquid crystal display panels comprising TFTs that use thin film transistors as switching devices for pixel electrodes. Additionally, TFTs using polycrystalline Si rather than amorphous Si are gaining popularity. Video signals for the level of resolution necessary to meet the NTSC standards that are used for the NTSC television system do not require high speed processing capabilities. Therefore, not only TFTs but also components of peripheral circuits including shift registers and decoders may be made of polycrystalline Si to produce a liquid crystal display apparatus wherein a display region and peripheral drive circuits are integrally formed.
However, the performance of polycrystalline Si is less than that of monocrystalline Si so that shift registers, for example, may have to be divided into a plurality of groups that are installed separately in order to realize a television set with a level of resolution higher than the level required by the NTSC standards or a computer display with the so-called XGA or SXGA class of resolution. Then, noise can appear as ghost along the boundaries of the separated devices in the display region to provide a problem to be solved.
In an attempt to bypass this problem, display apparatuses comprising a monocrystalline Si substrate having a high drive potential have been proposed to replace display apparatus of the above described integral type using monocrystalline Si. Since the drive potential of the transistors of the peripheral drive circuits of such display apparatus is satisfactory, the above described technique of dividing devices is not necessary here and hence the noise problem can be successfully avoided.
Liquid crystal display apparatus as described above are typically categorized into two types; the transmission type comprising a liquid crystal layer arranged between transparent electrodes for displaying images by controlling the transmission of incident light; and the reflection type for displaying images by providing a light-reflecting surface on the rear side substrate controlling the reflection of incident light.
As for the reflection type liquid crystal apparatus, the pixel electrodes arranged on the rear side substrate are patterned to show a matrix that has openings between any adjacently located pixel electrodes. As light enters through the openings, drive devices such as transistors arranged below the pixel electrodes and some of the peripheral circuits are irradiated with incident light to give rise to leak currents that adversely affect the image displaying characteristics of the apparatus.